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proautotech, Mechanic

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Chrysler: Got a p0420 mil CODE...egr valve..mileage etc...valve cover

Customer Question

Got a P0420 MIL CODE. Chrysler 2005 Town and Country 3.8L.

Brief History:

Between 100-150K miles.Fairly good maintenance.Recently replaced EGR valve for second time (just proactive for mileage etc.)Recently replaced rear valve cover gasketStill change with rec'd synthetic oil. 5W30\Regular spark plugs, oil changes, etc.O2 sensors, I simply can't remember, so I really don't know if they have ever been replaced - if they have certainly not recently at allOther than above, no major parts replaced and no engine rebuilt.Van used to get driven often, but for the past year+ it is driven very little. About every other day, but not many miles.

The van has been losing about a quart of oil at least every 2K miles or so. I thought it was all leaks, but with this new code I'm fearing it may have been burning some oil too. Seems this code usually means cat converter, but I would like to know my best bet. If it is the cat converter, what's the best plan, and converter to get? I plan on doing the repairs myself if possible as I have for several years now. Also, if the cat converter is bad from burning oil , then what the prospects for it lasting beyond replacement? Obviously , I'm hoping I won't have to do any engine rebuild to fix an oil burn. I don't see any oil burning in the exhaust, but I realize this may not be visible.

Other than the "slow" oil loss, the van runs OK as it usually does. I have other minor problems like a noisy slow speed steering that I've never been able to sort out, but other than that it is OK.

So, I'd like a best answer to the above question. Also, if it is something expensive like the cat converter, I'd like to know if I can drive it for awhile without fixing. I just reset the code tonight, so I don't know if/when it will throw again - but as murphy's law i'm sure it will soon again.

Thanks for trusting us with your problem. I have trained in the automotive field and currently work as a shop foreman. I will be helping you today.

proautotech :

A P0420 code means that the front and rear sensors are switching at nearly the same rate. Either the front O2 sensor is slow or the catalytic converter is faulty.

proautotech :

The vehicle will use some oil when it gets to the higher miles. But it maybe burning some oil from the rings. You could do a engine clean with seafoam. This may help. Synthetic oil runs much thinner so you may want to run a bottle of engine oil stabilizer. This may help it out with being thin. The seafoam may help the rings out enough to stop damage to the catalytic convertor.

proautotech :

You can get it done at a local exhaust shop to be easiest. They do not charge that much more than doing it yourself. You can buy a universal catalytic convertor they run about 100 bucks.

proautotech :

The steering noise is most likely worn out steering gear (rack and pinion) But I would not expect this to be anything to worry about in the near future. These vans are pretty famous for the noise.

proautotech :

You could replace the front O2 sensors. But the problem is more than likely the catalytic convertor.

A P0420 code means that the front and rear sensors are switching at nearly the same rate. Either the front O2 sensor is slow or the catalytic converter is faulty.

proautotech :

The vehicle will use some oil when it gets to the higher miles. But it maybe burning some oil from the rings. You could do a engine clean with seafoam. This may help. Synthetic oil runs much thinner so you may want to run a bottle of engine oil stabilizer. This may help it out with being thin. The seafoam may help the rings out enough to stop damage to the catalytic convertor.

proautotech :

You can get it done at a local exhaust shop to be easiest. They do not charge that much more than doing it yourself. You can buy a universal catalytic convertor they run about 100 bucks.

proautotech :

The steering noise is most likely worn out steering gear (rack and pinion) But I would not expect this to be anything to worry about in the near future. These vans are pretty famous for the noise.

proautotech :

You could replace the front O2 sensors. But the problem is more than likely the catalytic convertor.

1) What about the stuff I read where this vehicle is 99% the cat converter when this particular code is fired?2) Is there any danger of further damage running BEFORE fixing the problem?3) Would you honestly rec'd the O2 sensor first , or the cat converter? If the O2, which one , or both?4) What about the cat converter? I hear the DTC can be very picky, so do I need to get one from the dealer? If I can get from a place like advance auto, what brand/type?

I don't have a specific brand from the local parts store. They change all the time.

If you have a handheld scan tool you can properly verify the operation of the front O2 sensor. Like I stated above most likely it is the cat but if you want to be sure verify O2 sensor operation.

You can drive it as long as you would like. It can leave you stranded though. The backpressure is not good on anything. It will start causing overheating along with engine failure if the overheating is bad enough.

OK I'll accept this, but can you tell me what you mean by verifying the O2 with a hand scanner? I'm assuming I do not have one of these, as I just have an ODB code scanner. What would be the cheapest/easiest way for me to literally test the o2 sensor?

Oh man, well I suppose that would be useful in maintaining my Chrysler and 2000 SAAB, but $1000 for a tool is a lot of money. I guess at this point I could just replace the front O2 sensor and see what happens? Only thing I'm concerned about is somehow blowing the O2 sensor if I replace it without the cat converter and the problem winds up being the cat converter.

Yeah OK. Thanks for the tips! I do want to get one, but I'm thinking it may not be soon enough for this repair. So it sounds like I could just replace the O2 first. See if the code gets thrown again. If it does, then replace the cat converter. In this way I shouldn't risk causing overheat on the engine.

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